Automatic telephone system



1, 1927' w. A. BENSON 616338 ,AUTOMATIC TELEPHONE SYSTEM I Original Filed Feb. 11 1922 2 Sheets-Sheet l T0 TELL TIME H [q Q TLUEULUI Feb. 8 9 W. A. BENSON AUTOMATIC TELEPHONE SYSTEM Original Filed Feb. 11. 1922 2 Sheets-Shunt 2 Patented Feb. 8, 1927.

UNITE STATES'PATENT OFFICE.

WILLIAM A. BENSON, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS,

TO AUTOMATIC ELECTRIC INC., OF CHICAGO, ILLINOIS, A CORPORATION OF DELA- WARE.

AUTOMATIC TELEPHONE SYSTEM.

Application filed February 11, 1922, Serial No. 535,714. Renewed June 28, 1926.

This invention relates in general to automatic telephone systems, but more especially to automatic systems of relatively small size, or branch exchanges, such as are intended for use in small communities, and the size of which would not warrant the expense of employing an attendant.

All the maintenance in these small exchanges is usually handled from the distant main exchange, and formerly an operator at the main exchange, at specified time intervals, dialed a special number which automatically connected her with the alarm sys tem at the branch exchange. In systems of this kind the operator might forget to dial the branch exchange or some trouble might arise that would need immediate attention long before the time had arrived for the operator to call. In some other cases separate alarm leads to the main exchange are provided, but if the distance is too great this arrangement is object1onal.

The object of this invention 1s to trunk the alarm signal to the operator at the mam exchange over any of the connecting trunk lines in the same manner as an ordinary call to the main exchange, thus eliminating the necessity of requiring an operator to periodically dial the branch exchange, or the running of separate leads for the alarm.

One of the features of the invention is the operators supervision of trunk release whereby the operator, by removing her plug from the trunk jack after receiving the alarm signal, releases the switch from the trunk line, allowing the trunk line to be come idle so that it can be used for regular subscribers calls.

Another feature is the trunking of two different alarm tones to the operator at the main exchange through the same switch.

There are other features which together with the above will be described hereinafter, reference being had to the accompanying drawings, in which Fig. 1 diagrammatically represents an unattended private automatic exchange with trunk lines connecting with the main exchange, while Fig. 2 represents the operators switchboard in the main exchange.

At A in Fig. 1 is shown an alarm set which may be of any well known type comprising an alarm tone machine and contacts for two alarm circuits. The alarm tone machine consists of two interrupters 50 and 51 mounted on a common continuously rotating shaft, and two induction coils 52 and 53, said interrupters interrupting the circuit in the primary windings of their respective induction coils to produce in the secondary windings induced alarm tones which are transmitted over suitable conductors to the alarm switch.- The two alarm circuits are closed at contacts 2 and 3 in cases of trouble. For instance, in a typical case all of the apparatus in the branch exchange is fused by spring fuses to a common battery bus bar; directly below this bus bar is another small bus bar commonly.

known as the toll tale bus bar, which is located in such a position that when any fuse is blown, the spring of the blown fuse is released against the tell tale bus bar to connect battery thereto. The application of battery to the tell tale bus bar energizes the fuse alarm relay which in turn closes contact 3. The contact 2 is closed in case of various minor troubles in a manner similar to contact 3, as, for example, in case a proteeter heat coil blows at the main distributing frame.

The reference character B indicates an alarm switch similar in construction and operation to the well known rotary line switch of the type in which the wipers have no normal position and move in a forward direction only. This switch is actuated in cases of trouble to seize an idle trunk line and to transmit an alarm signal to the switchboard in the main exchange. Con ductors 46 and 49 are conductors of one of the trunk lines extending to the main exchange. Thesetrunk lines have bank multiples, a portion of whichare shown to the right of B and are accessible to the alarm switch and also to selector switches of the well known Strowger type such as are common in exchanges of this character, said selector switches to be used for outgoing calls to the main exchange as well as local calls. The reference character C indicates a line switch of the well known rotary type in which the wipers have no normal position and move in a forward direction only. The line switches C, only one of which is shown, are individual to the trunk lines extending to the main exchange and are used for incoming calls from the main exchange,

Certain of the slow-acting relays in Fig. 1 are slow to energize as well as slow to deenergize, a result which is secured by placing a copper slug on the armature end of the core. This distinction-is indicated in the drawing by showing the copper slug in black rather than by section lines.

Fig. 2 shows the manual equipment at the main exchange which is all old and which is included because of its cooperation with the re:t of the equipment. At J is shown an ordinary jack with the drop D. The reference character O indicates a portion of an operators cord circuit of a type which is in common use. Just above the cord circuit is shown the operators head set.

Having described the apparatus briefly I will now proceed to point out more in detail the novel features of this invention and explain the operation thereof. For this purpose it will be assumed that some minor case of trouble in the branch exchange has energized a relay to close the contact 2. When the contact 2 is closed an energizing circuit for relay 7 is established as follows: from ground G, by way of armature 2 and its working contact, armature 20 and its resting contact, and the winding of relay 7 to battery. Relay 7 is energized over the above traced circuit and at its upper armature 26 the circuit for the rotary magnet 13 is closed and at its lower armature 29 the circuit for the switching relay 12 is prepared in series with the rotary magnet. The operation now depends upon whether the trunk line with which the alarm switch wipers are associated is busy or idle. If the trunk line is busy there is a ground potential upon the test contact with which the test wiper 5 1 is in engagement, the switching relay 12 is short circuited, and the rotary magnet 13, which interrupts itsown circuit, is operated in the manner of a buzzer to advance the switch wipers until an idle trunk line is found. lVhen the switch wipers come into engagement with an idle trunk line, the one shown in the drawing, for instance, the rotary magnet ceases to operate and at the same time the short circuit around the switching relay 12 is removed, since the test wiper 54 no longer finds a ground. lVhen the short circuit around relay 12 is removed, said relay is energized over the following path: ground by way of the working contact of armature 29 and said armature, winding of switching relay l2, interrupter springs of the rotary magnet and through the winding of said magnet to battery. The rotary magnet, however, is not energized in series with the switching relay due to the high resistance of said switching relay. The switching relay, upon energizing, grounds the test wiper 54 and opens the circuit for the rotary magnet at its armature 37 prepares the ringing circuit for the drop at the operators switchboard in the main exchange at its armatures 36 and 38, and at its armature 39 closes an energizing circuit for the ringing relay 14;. By means of the ground potential placed on the test contact 55, the switching relay 15 of the individual line switch C is energized to clear the trunk line of its normal battery and ground connections at the line switch. The busy potential also extends to the multiple test contacts of the selector switches for rendering said trunk line busy to all said selector switches having access thereto.

The ringing relay 14 is a high resistance relay having a stiff spring adjustment and a copper slug on the heel end of the core to make said relay slow to energize. The ringing relay is made slow acting to avoid the possibility of the generator being temporarily short circuited at the resting contact of armature 56 of relay 15. Shortly after the relay 15 is energized the ringing relay is also energized. Generator is now applied to the trunk line for signalling the operator at the main exchange over the following path: free pole of generator, working contact of armature 40 and said armature, resting contact of armature 33 and said armature, armature 38 and its working contact, wiper 47, bank contact 48, trunk conductor 49, condenser 57, winding of drop D, contact 58, trunk conductor 16, bank contact 45, wiper 43, working contact of armature 36 and said armature, armature 32 and its resting contact, armature 4:1 and its working contact to ground. The drop D is operated over the above traced circuit.

At the same time enerator is applied to the trunk line an energizing circuit for relay 8 is completed at armature A2 and its working contact. Relay 8 is similar in construction and operation to the relay disclosed in the J. Erickson application, iiled Dec. 31., 1919, Serial Number 348,548. lVhen said relay attracts its arn'lature the weight attached to spring 31 starts to vibrate. which rapidly closes and opens the circuit for relay 9 at the contacts of the springs 30 and iii. The relay 9, however, due to its heigh in'ipedance does not fully energize until its circuit is permanently closed. When the weight on spring 31 stops vibrating the circuit for relay 9 is permanently clased allowing said relay to operate. Relay 9 at its armatures and 33 disconnects generator from the trunk line and at its working contacts prepares the circuit forrelay 10.

\Vhen the operator in the main exchange at. whose position the drop 1) appears perceives the signal she will answer said signal by inserting the answering plug of an idle cord circuit, cord circuit 0 for example, in the jack J. As a result the relay 10 is en.- ergized over the following path: ground, upper winding of relay 10, working contact of armature 32 and said armature, armature 36 and working contact, wiper 43, bank contact 45, trunk conductor 46, tip contact of jack J, tip of plug, upper resting contact of dialling key, upper winding of repeating coil, polarized relay 18,lower winding of repeating coil, lower resting contact of dialling key, ring of plug, ring contact of jack J, trunk conductor 49, bank contact 48, Wiper 47, working contact of armature 38 and said armature, armature 33 and its working contact, lower Winding of relay 10 to battery. Relay 10, at its armature 34 and its working contact, completes an energizing circuit for slow to release relay 11.

WVhcn the operators listening key is thrown she will hear the minor trouble alarm tone in her headset, the tone being transmitted over a circuit. extending as follows: ground, secondary winding of induction coil 53, condenser 59, working contact of armature 27 and said armature, restng contact of armature 24 and said armature, working contact of armature 32 andv said armature, armature 36 and its working contact, wiper 43, bank contact 45, trunk conductor 46, through the operators cord circuit and headset, and trunk conductor 49 to battery at the lower winding of relay 10 as previously traced. The operator then notifies the attendant at the main exchange of the nature of the trouble at the branch exchange and removes her cord circuit 0 from the jack J. When the operators cord circuit is removed from the jack the circuit for relay 10 is opened, and said relay is deenergized. The circuit for relay 11 is opened at armature 34 and its working contact, but said relay is slow to deenergize, and maintains its armature in an operated position long enough to complete an energizing circuit for relay 4, which may be traced from ground, armature 34 and its resting contact, armature 85 and its working contact, armature 28 and its working contact, and winding of relay 4 to battery. Relay 4 energizes and locks itself up at armature 20. At armature 20 also the circuit for relay 7 is opened and said relay is deenergized. Upon the deenergization of relay 7 the following circuits are opened: the alarm circuit at armature 27, the circuit for the rotary magnet at armature 26, the original energizing circuit for relay 4 at armature 28, and at armature 29 the circuits for relays 12 and 14. On deenergizing, relay 14 opens the circuit of relay 8. Relay 8 then deenergizes and in turn deenergiz-es relay 9. When relay 12 deenergizes it removes ground from the test wiper 54 thereby leaving the trunk line with which the wipers are in engagement idle and ready for subscribers calls. The relay 4 is maintained energized until the trouble at the branch exchange has been remedied.

If a fuse should blow before the first mentioned trouble has been remedied the following operation takes place. The fuse alarm relay energizes in the manner previously explained and closes contact 3, thus completing an energizing circuit for relay 6, which may be traced from ground, Winding of relay 6, resting contact of armature 21 and said armature, and contact 3 to battery. As will be noted, relay 6 closes circuits at its armatures 25 and 23, for the rotary magnet 13 and the switching relay 12, from which it will be understood that the operation of the switch is the same as has been previously explained. When generator again rings down the drop at the operators position, the operator answers in the usual manner and this time hears the fuse alarm tone over the following path: from ground, secondary winding of the induction coil 52, condenser 60, Working contact of armature 24 and said armature, working contact of armature 32 and said armature, over the trunk line, through the operators cord circuit and head-set, and back to battery at relay 10 as previously traced. The operator then notifies the attendant at the main ex change of the nature of the trouble at the branch exchange and removes her plug from the jack. Relay 10 is again d-eenergized and this time an energizing circuit for relay 5 is temporarily established by way of armature 35 and its working contact, and armature 22. Relay 5 immediately locks itself through its upper winding, and is main tained energized until the trouble is remedied. At armature 21 and its resting contact the circuit for relay 6 is opened and said relay is deenergized, whereupon the switch is again released from the trunk line in the same manner as previously described.

Having described the invention, what I consider to be new and desire to have protected by Letters Patent will be pointed out in the appended claims.

What I claim is:

1. In a telephone system, a main exchange, a branch exchange, trunk lines interconnecting said main and branch exchanges, a switch, an alarm set in said branch exchange, means responsive to the occurrence of a case of trouble at the branch exchange for operating said alarm set, said trunk lines terminating in an operators switchboardat said main exchange, and means controlled by said alarm set for actuating said switch to seize an idle one of said trunk lines.

2. In a' telephone system, a main exchange, a branch exchange, trunk lines interconnecting said main and v branch exchanges, a switch, an alarm set in said branch exchange and means for operating the same automatically responsive to a case of trouble occurring at the branch exchange, said trunk lines terminating in an operators switchboard at said main exchange and having signals individual thereto, and means controlled by said alarm set for actuating said switch to seize an idle one of said trunk lines and to operate the signal individual thereto.

3. In a telephone system, a main ex change, a branch exchange, trunk lines intel-connecting said main and branch exchanges, a switch, an alarm set in said branch exchange and means for operating the same in case of trouble, said trunk lines terminating in an operators switchboard at the main exchange, means controlled by said alarm set for actuating said switch to seize an idle one of said trunk lines, and means controlled at said main exchange for disconnecting said switch from said trunk line.

4. In a telephone system, a main exchange, a branch exchange, trunk lines interconnecting said main and branch exchanges, a switch, an alarm set in said branch exchange and means for operating thesame in case of trouble, said trunk lines terminating in an o-perators switchboard at said main exchange and having signals individual thereto, means controlled by said alarm set for actuating said switch to seize an idle one of said trunks and to operate said signal individual thereto, and means controlled at said main exchange for disconnecting said switch from said trunk line.

5. In a telephone system, a main exchange, a branch exchange, trunk lines interconnecting said main and branch exchanges, a switch, an alai'nrset in said branch exchange and means for operating the same in cas of trouble, said trunk lines terminating in an operators switchboard at said main exchange, and means controlled by said alarm set for actuating said switch to seize an idle one of said trunk lines, and to transmit a distinctive alarm signal over said trunk line to the operator at said switchboard to indicate the character of the trouble.

(5. In a telephone system, a main exchange, a branch exchange, trunk lines interconnecting said main and branch exchanges, a switch, an alarm set in said branch exchange and means for operating the same in case of trouble, said trunk lines terminating in an operators switchboard at said main exchange and having visual signals individual thereto, means controlled by said alarm set for actuating said switch to seize an idle one of said trunk lines and to operate said. visual signal individual thereto, and means controlled by said switch for transmitting an audible alarm signal over said trunk line to the operator at said switchboard.

7. In a telephone system, a main exchange, a branch exchange, trunk lines interconnecting said exchanges, a switch having access to said trunk lines, said trunk lines terminating in an operators switchboard at the main exchange, an alarm set in said branch exchange aud means for operating the same in cases of trouble, means controlled by said alarm set for actuating said switch to seize an idle one of said trunk lines, means controlled by said switch when one of said trunk lines is connected with for momentarily applying signal current to said trunk line to signal the operator at said switchboard in the main exchange, means controlled by said switch for permanently disconnecting said signal current from said line after a predetermined period, and means for transmitting a signal over the trunk line to notify the op erator of the nature of the trouble.

8. In a telephone system, main and branch exchanges, trunk lines for use by the branch exchange subscribers in calling the main exchange, an alarm switch at the branch exchange having access to said trunk lines in common with the subscribers switches, and means for automatically operating said alarm switch to connect with an idle one of said trunk lines whenever a particular variety of trouble occurs at the branch exchange.

9. In a telephone system, main and branch exchanges, trunk lines for use by the branch exchange subscribers in calling the main exchange, an alarm switch at the branch exchange having access to said trunk lines in common with the subscribers switches, means for automatically operating said alarm switch to connect with an idle one of sald trunk lines whenever a particular variety of trouble occurs at the branch exchange, an operators switchboard in the main exchange, and means for signalling the operator at said switchboard over the selected trunk line.

10. In a telephone system, main and branch exchanges, trunk lines for use by the branch exchange subscribers in calling the main exchange, an alarm switch at the branclrexchange having access to said trunk lines in common with the subscribers switches, means for automatically operating said alarm switch to connect with an idle one of said trunk lines whenever a particular variety of trouble occurs at the branch exchange, an operators switchboard in the main exchange, means for signalling the operator at said switchboard overthe selected trunk line, and means for transmitting a distinctive tone signal to the operator over said trunk line to notify her of the nature of the trouble.

11. The combination, with an automatic exchange and an operators switchboard, of trunk lines for use in connecting automatic subscribers lines with said switchboard, a signalling machine, and means operated automatically responsive to the occurrence of a case of trouble in the automatic exchange for connecting said machine with an idle one of said trunk lines.

12. In a telephone system, an automatic exchange, an operators switchboard, trunk lines extending from said exchange to said switchboard, automatic switches included in said exchange and controlled by calling parties for extending connections to said switchboard over said trunk lines, and an alarm switch in said exchange operated automatically responsive to the occurrence of a case of trouble in the exchange to connect with an idle one of said trunk lines and render the same busy to said first mentioned switches.

13. In a telephone system, an automatic exchange, an operators switchboard, trunk lines extending from said exchange to said switchboard, automatic switches included in said exchange and controlled by calling parties for extending connections to said switchboard over said trunk lines, an alarm switch in said exchange operated automatically responsive to the occurrence of a case of trouble to connect with an idle one of said trunk lines and signal the operator thereover, and means for giving the operator a distinctive signal to notify her that the call was originated by a case of trouble rather than by a calling subscriber.

14. In a telephone system, an automatic exchange, an operators switchboard, trunk lines accessible to automatic switches in said exchange and extending to said switchboard, an alarm switch operated responsive to the occurrence of a case of trouble in the auto.- matic exchange to connect with an idle one of said trunk lines and make the same busy to said first mentioned switches, and means for signaling the operator over the connected trunk line in a distinctive manner to advise her that the call was originated by a case of trouble rather than by a calling subscriber.

15. In a telephone system, automatic switches controlled by calling subscribers, another switch operated automatically responsive to the occurrence of a case of trouble and independent of subscriber control, and a group of trunk lines accessible 1n common to all said switches.

16. In a telephone system, automatic switches controlled by calling subscriber, another switch operated automatically responsive to the occurrence of a case of trouble and independent of subscriber control, an operators switchboard, a group of trunk lines accessible to all said switches 111 common for extending calls to said switchboard,

in said switching apparatus for operating said alarm set, an operators switchboard at said main exchange terminating said trunk lines, and means controlled by said alarm set for actuating said switch to seize an idle one of said trunk lines.

18. In a telephone system, a main exchange, a branch exchange, trunk lines interconnecting said main exchange and branch exchanges, a switch, an alarm set in said branch exchange, means responsive to the blowing of a fuse in said branch exchange for operating said alarm set, an operators switchboard at said main exchange terminating said trunk lines, and means controlled by said alarm set for actuating said switch to seize an idle one of said trunk lines.

19. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at the first switchboard automatically responsive to an abnormal condition at said. first switchboard, antomatic switching mechanism at said first switchboard, and means controlled by said alarm set when it responds for operating said mechanism to effect a connection between said alarm set and the second switchboard via any idle one of said trunk lines.

20. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at the first switchboard automatically responsive to an abnormal condition at the first switchboard, an automatic switch individual to said alarm set, means controlled by said alarm set when it responds for operating said switch to extend a connection to the second switchboard via an idle one of said trunk lines, ring down signals on said trunk lines at the second switchboard, and means associated with said switch for momentarily applying ringing current to the seized trunk line to operate the ring down. signal thereon at the second switchboard.

21. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at the first switchboard automatically responsive to an abnormal condition at the first switchboard, an automatic switch, means controlled by said alarm set when it responds for operating said switch to extend a connection to the second switchboard via an. idle one of said trunk lines,

22. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at the first switchboard automatically responsive to an abnormal condition at the first switchboard, an. automatic switch individual to said alarm set, means controlled by said alarm set when it responds for operating said switch to extend a connection to the second switchboard via an idle one of said trunk lines, ring down signals on said trunk lines at the second switchboard, means in said switch for applying ringing current to the seized trunk line, and a timing device individual to the switch for subsequently removing the ringing current.

23. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at the first switchboard automatically responsive to an abnormal condition at the first switchboard, an automatic switch individual to said alarm set, means controlled by said alarm set when it responds for operating said switch to extend a connection to the second switchboard via an idle one of said trunk lines, ring down signals on said trunk lines at the second switchboard, a battery feed relay in said switch, means in said switch for applying ringing current to the seized trunk line momentarily and for then connecting up said battery feed relay to the trunk line. Y

24. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at the first switchboard automatically responsive to an abnormal condition at the first switchboard, an automatic switch individual to said alarm set, means controlled by said alarm set when it responds for operating said switch to extend a connection to the second switchboard via an idle one of said trunk lines, ring down signals on said trunk lines at the second switchboard, a battery feed relay in said switch, means in said switch for applying ringing current to the seized trunk line momentarily and for then connecting up said battery feed relay to the trunk line, means at the second switchboard for completing a connection to the seized trunk line and for operating said battery feed relay, and means controlled by said battery feed relay when it falls back when the connection at the second switchboard is broken for releasing said alarm switch and for thereby freeing the trunk line.

25. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at the first switchboard automatically responsive to an abnormal condition at the first switchboard, an automatic switch individual to said alarm set, means controlled by said alarm set when it responds for operating said switch to extend a connection to the second switchboard via an idle one of said trunk lines, a battery feed relay in said switch, means at the second switchboard for completing a connection to the seized trunk line and for operating said battery feed relay, and means controlled by said bat-tery feed relay when it falls back when the connection at the second switchboard is broken for releasing said. alarm switch and for thereby freeing the trunk line.

26. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at said first switchboard automatically responsive to either of two abnormal conditions at the first switchboard, au-- tomatic switching mechanism at said first switchboard, means controlled by said alarm set when it responds to either abnormal condition for operating said mechanism to effect a connection between said alarm set and the second switchboard via an idle one of said trunk lines, means associated with said switch for transmitting over the seized trunk line an indication of the particular instant abnormal condition. means for subsequently releasing said mechanism and for rendering it non-responsive to the continued existence of the abnormal condition, and means responsive automatically to the other abnormal condition at the switchboard in case it occurs for operating said mechanism to complete a second connection to said switchboard via an idle one of said trunk lines.

27. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at said first switchboard automatically responsive to either of two abnormal conditions at the first switchboard, automatic switching mechanism at said first switchboard, means controlled by said alarm set when it responds to either abnormal condition for operating said mechanism to effeet a connection between said alarm set and the second switchboard via an idle one of said trunk lines, means associated with said switch for transmitting over the seized trunk line an indication of the particular instant abnormal condition, means for sub sequently releasing said mechanism for rendering it non-responsive to the continued existence of the abnormal condition, means responsive automatically to the other abnore mal condition at the switchboard in case it occurs for operating said mechanism to complete a second connection to said switchboard via an idle one of said trunk lines, and means associated with said switch for transmitting over the seized trunk line an indication of the last named abnormal condition.

28. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for use in completing telephone connections therebetween, an alarm set at said first switchboard automatically responsive to either of two abnormal conditions at the first switchboard, automatic switching mechanism at said first switchboard, means controlled by said alarm set when it responds to either abnormal condition for operating said mechanism to effeet a connection between said alarm set and the second switchboard Via an idle one of said trunk lines, means for subsequently releasing said mechanism and for rendering it non-responsive to the continued existence of the abnormal condition, means responsive automatically to the other abnormal condition at the switchboard in case it occurs for operating said mechanism to complete a second connection to said switchboard via an idle one of said trunk lines, and means for releasing the second connection and for rendering said mechanism non-responsive to the continued existence of the second abnormal condition.

29. In a telephone system, a first switchboard, a second switchboard, trunk lines connecting said switchboards for-use in completing telephone connections therebetween, an alarm set at said first switchboard automatically responsive to either of two abnor mal conditions at the first switchboard, an automatic switch individual to said set, means controlled by said alarm set when it responds to either abnormal condition for operating said switch to effect a connection between said alarm set and the second switchboard via an idle one of said trunk lines, means for transmitting over the seized trunk line in either case an indication of the particular instant abnormal condition, and means for subsequently releasing said switch in either case and for rendering it non-resnonsive to the continued existence of the abnormal condition, whereby said switch is placed in condition to respond automatically to the other abnormal condition at the switchboard in case it occurs.

In witness whereof, I hereunto subscribe my name this th day of February, A. D. 1922. I

WVILLIAM A. BENSON. 

